In recent years, hybrid vehicles powered by an engine and a motor have become popular due to environmental requirements such as low fuel consumption and low exhaust gas emissions. Hybrid vehicles may have several driving modes to switch between including (i) an engine travel mode, in which the vehicle travels on a drive power only from an engine, (ii) an EV travel mode, in which the vehicle travels on a drive power only from a motor generator, (iii) an MG assist mode, in which the vehicle travels on a drive power from both of the engine and the motor generator, and (iv) an engine generation mode, in which the engine is used to provide both drive power to the vehicle and generate electricity by using the motor generator.
For example, in a patent document 1 (i.e., Japanese Patent Laid-Open No. JP-2007-176270A), an operation of the motor generator for generating electricity and an operation of the motor generator for driving the vehicle are compared with each other, in order to determine which one of those two operations creates greater economic benefits than the other. Then, based on a comparison result, an instruction command for operating the motor generator in a more economic mode is sent to the motor generator.
However, the patent document 1 is silent about the economic benefits of the EV travel mode in which the vehicle travels only on drive power from the motor generator but not drive power from the engine.